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RADIO COMPASS COMPENSATOR Filed June 2, 1924 isY ` l l vRefciii'ingto the drawin vthe radio compass' installation' L Patented Aug. 20, 19%.

UNITI-:D STATES 'PATENT carica.

Y FBEDRICX A. HOLSTER, OF PALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- l GBAIH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A. CORPORATION OI' CALI- FORNIA.

RADIO COMPASS COMPENBATOB.

v Application tiled June 2, 1924. Serial No. 717,893.

This invention relates to radio compass and more particularly iq the elimoperixtoi2 inati o errors that arise in connection with that may be used for example on ship ard,

all of them so far as I know, are subject to errors arisi fromv thel character 'qf the ships mass; t is effect may be attributed to ythe changes in wave front as it strikes the ship, whereby the apparent bearing of a distant source of radiations, as determinedby the radiocompass reading, diii'ers slightly from the correct one. vIt is one of the dolijects of my invention to eliminate o r minimize so that if any error at all remains, it wil be of an entirely. different order of magnitude and readil compensated for by other means. vI lshall escribe in this application an emhodjmeiit-of vmy invention operating on 4e, radio compass` receivin circuit having a loop or coil acting as an asorber; such systems are usually in the form-of a vertical, rotatzably mounted coil having the so-called figcharacteristic. Further-` mgeeinvention to aure directional more, the 'application of A.shipboard installation has n found particularlyadvantageous, due to the peculiar nature of theerrors caused by the metallic mass of the ship and its accessories.

1 My invention possesses other advantageous features,some of which, with the fore ung, wiii be sa forth a length in the 01- -lowing description, where I shall outline in full that form of the invention which I have selected for illustration in the drawings ac c0111 an and formin part of the presvent 'Epplilclgtiom Although I have shown in the drawings` but one form of the invention, y I do net desire to be limited thereto, since the invention as expressed in the claims 'ma beembodiedinother formsalso.

l Fig. 8 isa curve error due to change` in wave fronti' circuitsz as indicated by "the fact sition of the coil characteristic of the type of radio compass illustrated in the former ligure; and

Fi' 4 shows a set o f curves by which it is possi le to demonstrate the present invention.

In the form of radio compass that I have chosen for illustration, there is a rotatable coil 11 of a few turns, the axis of the coil utility of the being substantially horizontal, and its axis of rotation being vertical and at right angles i to the'coil axis. The arrangement is such that whenithe coil 11 has its plane pointin toward a source of radiations, the stren E The direction ofthe source may thus be determined. The plane of the coil refers to 'that plane which intersects the axis at right agles, at'the geometrical centre of the coil.'

- en use is made of such a coil forabsorb- 'of the signals received diiers substantie y `rom that received in Othercoil positions.

ing electromagnetic-radiations, the direel 4tional characteristicfof the coil mayl be'rep# resented by a figure 8, such as illustrated in Fig. 3. If the coil 11v is assumed to be at the arallel tothe line 1 12, "and if. a source of ra 'ations falls in line point o, with .its plane 12, either above or below the point o, there will be a maximum response xrthe receiver line 12 intersects the two loops of the gine 8 at the points 13 and 14, which 'are fa est distant. from the point o representing'the pol. Sources disposed other radial line extending from point o, such as 17 will cause a nse the extent of which is indicated by e length o of the radius included between the point o and the ligure 8, and drawn in the direction ofthe source. As the departure from line 12 comes that the" many.v

nearer and nearer to the line 18, rpendicular to the plane of coil' 11, the-lessdoes the response become, until at line 18 the re-l onseis a minimum. This minimumfcoirv tion corres nds to the tposition ordinarily utilized for etermining irection. lForthia purpose, coil 11 is slowly rotated while the response is noted and when'it becomes a' the co 11 is known to'liave its axis n toward the source, or in other that its plane perpendiciilarvto the In rig. ses @enneagram n indigena. for 'the apparatus. The coil-1.1

weA

forms an element of a non-uniform absorption system, which is tuned to resonance by the aid of the variable condenser i5 in series with the coil. Ar detector circuit connected across the coil ll indicates the degree of response in any well-lmown manner.

Since the radio compass as thus described is also known, further description ci its operation is considered unnecessary.

. As shown in Fig. 1, the compass coil li is usually mounted on top of an enclosure 2l on the upper deck of the vessel 22. When located on such a vessel, it has been found that the metallic mass thereof deiects the wave ro'ntof the radiations received by the coil.

This -effect introduces an error that is considerable, and cannot be ignored. IThus when these errors exist, the con axis, 1n-

stead or pointing toward the source, must be turned through a small angle away from that position to secure minimum response in the detector circuit 20. The character of this error` may be understood from a considera.- tion of Fig. 4. Curve 23 represents the calibration curve o? such a compass. The abscissee of this curve represonty the number of angular degrees a source of radiations is displaced from the longitudinal axis nof the ship, which source is to affect the radlo compass. The ordinates represent the errors of the compass readings corresponding to these relative positions of the source and the ve."-

sel. For example, when the source is parallel or perpendicular to the longitudinal axis of the vessel 22, the errors are reduced to zero, as indicated at the points marked 0, 90,

180, 270, and 360'. However, at interinodiate positions of the source, the errors fluctuate someyvhat in the manner of a sine curve, being for example positive and of varying values between 0- and 90, as well as between 180 and 270, whileit is negative and of varying values between 90 and 180,

aswell as between 270 and 360. v

These errors of course could be determined and plotted, and the roper corrections applied to the readings, ut such a course is not only time consuming and laborious, but likely to lead to errors that may produce serious and irreparable injury. To overcome these disadvantages, I provide an arrangement whereby the directionV of the wave front is seemingly operated upon before it can aect the compass, such manner that it no longer causes errors inthe compass. In other words, the correction. is applied to supple- 'ment the radiations themselves, and the cor- Whatever 4errors do remain can'very readily be taken care of in other ways, not necessary at this time to describe.

The arrangement by which I am enabled to eect these highly beneficial results, includes the placin of an auxiliary non-uniform absorbing circuit in proper relation to the compass coil l1, so as to affect it by magnetic coupling; For example, I may use the stay wire 25 extending between the stacks of the vessel to serve as part of a systcm absorbing energy from the radiations. This wire is close enough to the to of coil 11 to act as a primary for it. In ot er words, current flowing in wire 25 has its counterpart in current induced by transformer action in coil ll. The wire 25 thus ailects the radio compass by inductive coupling. Furthermore, I find that to secure the neutralizing eiiect, the wire 25 should be parallel tol the longitudinal axis of the shi may form merely one side or" a oo ing circuit, the remainder comprising the metallic stacks 24, and the hull of vessel22.

In fact, it is possible to substitute for the arrangement described, other forms of loop 22, and if; absorbcircuits which directly absorb the radiations,

and transfer at least some of its energy by appropriate coupling to the radio compass coil. To regulate the effect of this compeneating arrangement, it is of .course necessary to choose the position of thecompensatingloop properly with respect to the surround-` ings, whether on shipboard or on land, and to design this loop circuit with the proper amount of resistance for the best eiect.

This latter requirement may easil be .ful-

filled by using a selected size and ength of stay wire. A high resistancel is to be preferredin order to make the compensating ,loop as perfectly aperiodic as practicable, so

that no material variation in the character of the response with varying frequencies may occur. l

The operation of the 'compensating arrangement may readily be describedin connection with Fig. 4. When the plane of coil 11 is perpendicular to the axis of the ship 22 and in position to respond to a minimum i .in inductive coupling. The result is that for this condition the compensation is zero, as it should be. imilarly, when the source is iu a line perpendicular to the axis of the vessel 22, the error is again zero, as indicated at the 90 ypoint of curve 23. The compensation is also zero, for the loop of which wire 25 is a part, is in proper position with the zero error positions, the current induced in coil 11 from wire 25 is in such phase relaindications,

tion that it o poses the error. This effect is shown by the light line curve 19 of Fig. 4. By proper choice of constants of the loop of which wire 25 forms a part, the compensation ma be made substantially com lete for all positions of the source. This is indicated in Fig. 4 by the fact that the ordinates of curve 19 are equal but opposite in sign to those of curve 23.

I claim: `1. The. method of reducin errors in a radio compass having a rotata le coil acting as an absorber of electromagnetic radiations.

and mounted in proximity to conductive masses which act on the radiations in such manner as to cause errors in the compass which comprises absorbin energy in an absorbing circuit including sai masses, from `the same source from which the coil absorbs energy, and coupling said absorbing circuit to the coil in such manner that energy is transferred thereto which compensates for the error.

2. In a radio compass, a rotatable coil acting as an absorber of electromagnetic radiations, and adapted to be brought to a position indicating the direction of a source of radiations by the character of its response tothe radiations, and meansfor compensating for errors in the indications, comprising an absorbing circuit in the form of a' loop inductively coupled to the coil and including conductive masses effecting said errors.v

3. In a radio compass, a rotatable coil acting as an absorber of electroma etic radiations, and adapted to be broug t to a position indicatin the direction of a source of radiation by t e character of its response to the radiations, and means for compensat-.

` ing for errors in the indications, com rising vwave front of the receiv `a. stationary loop including con uctive masses effecting said errors absorbing energy from the-same source as the coil, and arranged to be inductively coupled to the coil to transfer ener thereto, the extent of said coupling depen 1n upon the relative position of the coil an loop.

4. In a radio compass a directional coil dispose in proximit to conductive masses causigv distortion o energy and rotatable with respect to the bearing of the source fstem comprisingv the' of `said energy and with respect to said masses, and a closed circuit fixed with. respectv to said masses and comprising at least a portion of said masses, the method which comprisin at least a portion of said masses' and a con uctor disposed substantially arallel to the fore and aft line of the s "p, the method which com rises effecting between said conductor andpsaid coil a coupling of a character compensating for errors due to wave front distortion. l

6. A radio compass system comprising a circuit including a coil rotatable with respect to the bearing of a source of electro-magnetic radiations and disposed adjacent masses causing distortion of the wave front of,

enel' from said source, and a fixed circuit inclu ing at least a portion of said masses and so inductively related to the circuit of said coil as to compensate for error due to wave. front distortion for different positions of said coil.

7. A radio com ass system comprising. a coil rotatable wit respect to the bearing of a source of electro-magnetic radiations and disposed adjacentv masses causing distortion of the wavefront of energy-,from udinga said source, and a fixed circuit inc conductor and at least a' portion of said masses, said coil so disposed with t to said conductor as to eifect therewit a error due to wave front distortion for different positions of said coil.

8. A ships radio compass system comprising a circuit including a coil rotatable with respect to thebearing of a source of electromagnetic radiations and disposed adjacent masses causing distortion of the wave front of ener from said source, and a circuit fixed wit respect to the ship and including at least a portion of said masses and a conductor disposed substantially parallel to the fore and aft line of the ship said circuits bein so related as to elect therebetween a coup 'ng of a character to compensate for error due to wave front distortion for different positions of said coil.

9. A directional radio receiving system comprising a closed tunable circuit includ-4 ing a rotatable coil absorbing directl from a natural medium energy radiated' m a lao " comprising a cl indnctively relnted to said s for com-l circuit having a. directional characteristic disposed in xed tive relation to sai coil, and of high resist ance to com ensatefor eect of wave frontdistortion tliroughout the ringe for which said first circuit is tunable.

In testimony whereof, I have hereunto set my hand. I

FREDERICK A. KOLSTER sition in direct induc- 

